Polyethylene stabilized with a synergistic stabilizer combination



United States Patent 3,396,143 POLYETHYLENE STABILIZED WITH A SYNER- GISTIC STABILIZER COMBINATION Gordon C. Newland and John W. Tamblyn, Kmgsport,

Tenn., assignors to Eastman Kodak Company, Rochester, N .Y., a corporation of New Jersey No Drawing. Filed Jan. 22, 1965, Ser. No. 427,476

5 Claims. (Cl. 260-41) ABSTRACT OF THE DISCLOSURE A UV stabilized white thermoplastic composition comprising polyethylene and a synergistic stabilizer combination consisting essentially of a .pigmenting amount of TiO and 0.11.0% of 4,4 bis(2,6-di-t.-butyl-phenol), 2,2 methylene bis[6-(l-methylcyclohexyl)-p-cresol], or zinc N,N-di(C;-C alkyl) dithiocarbamate.

This invention resides in the chemical arts. It relates to synthetic resins and to the problem of inhibiting their deterioration under ultraviolet light.

Normally solid polymers of l-olefins, such as normally solid polyethylene and crystalline polypropylene, are thermopiastic, synthetic resins which have gained widespread use as materials of construction. However, as is well known, normally solid, l-olefin resins undergo photochemical degradation when exposed to ultraviolet light. This effect is frequently termed weathering. It appears to be a photooxidation process which causes rupture of the polymer chains and formation of carbonyl 0:0) groups. As this degradation progresses, articles manufactured from l-olefin resins tend to crack, become brittle and lose tensile strength to the extent of mechanical failure. White plastic compositions are often wanted. Such compositions are normally made by incoroporating va white pigment such as finely divided titanium dioxide, finely divided zinc oxide and the like into plastics by conventional mixing procedures. Unfortunately, these pigments offer very little protection against ultraviolet light degradation. Indeed, when finely divided titanum dioxide, for example, is incorporated into polyethylene, the result is an acceleration of ultraviolet light degradation.

This invention is based upon the discovery that certain mixtures of finely divided titanium dioxide and specific organic compounds, when incorporated into particular l-olefin resins, not only enhance the weatherability of these resins, but do so synergistically.

In summary, this inventioncomprises a normally solid, white, thermoplastic composition consisting essentially of (A) normally solid, l-olefin resin selected from the group consisting of normally solid polyethylene, normally solid polypropylene and normally solid copolymer of propylene and l-butene, (B) finely divided titanum dioxide at a concentration sufiicient to substantially pigment said 1- olefin resin and (C), whensaid l-olefin resin is normally solid polyethyene, 0.l-l% by weight of said resin of material selected from the group consisting of 4,4'-bis- (2,6 di t butylphenol), 2,2' methylenebis[6-(l-methylcyclohexyl) p cresol] and zinc N,N-di(C C alkyl) dithiocarbamate, when said l-olefin resin is normally solid polypropylene, 0.ll% by weight of said resin of material consiting essentially of p-t-butylphenol and, when said l-olefin resin is normally solid copolymer of propylene and l-butene, 0.1l% by weight of said resin of material selected from the group consisting of p-tbutylphenol, 2,2 methyleue-bis[6 (1 methylcyclohexyl)-p-cresol], zinc N,N-di(C C alkyl)dithiocarbamate, 4,4 bis(2,6-di-t-butylphenol), 4,4-butylidene(6- t butyl-m-cresol), 4,4'-thiobis(6-t-butyl-m-creso1) and N,N-diphenyl-p-phenylenediamine.

Normally solid polyethylene, normally solid polypropylene and normally solid copolymer of propylene and l-butene are well known l-olefin resins and, therefore, need not be further described herein. 7

Titanium dioxide is a well known white pigment. In general, it is a finely divided solid commercially available in at least two crystalline forms, the anatase and rutile forms. The concepts of this invention include both forms. A concentration of finely divided titanum dioxide in the composition of this invention generally of about 0.25-l0% by weight of the l-olefin resin is usually sufiicient to substantially pigment it.

The remaining components of the basic composition of this invention are well known compounds and, therefore, need not be further described herein.

The normally solid, thermoplastic composition of this invention can also comprise other additives such as, for example, antioxidants, heat stabilizers, additional ultraviolet light inhibitors, anticorrosion additives, antistatic agents, foaming agents, plasticizers, waxes, mold release agents, slip agents, anti-blocking agents, fillers, extenders and the like, including physical property improvers other than polymeric compounds.

The plastic composition of this invention is made by incorporating the components thereof into the l-olefin resin. Generally such incorporation is performed by any one of a number of well known methods, such as roll compounding, extrusion, solvent mixing and the like. For example, such incorporation can be performed by heating or otherwise softening the l-olefin resin to a workable consistency and then working in as by roll compounding until a substantially uniform mixture or dispersion is obtained.

The resulting plastic composition of this invention is then usually formed into articles such as pellets, sheeting, films, bars, tubes, filaments, specially shaped articles and the like as by conventional casting and molding techniques which include extrusion, compression molding, blow molding and the like.

This invention is further illustrated by the following examples of various aspects thereof including specific embodiments. Unless otherwise indicated this invention is not limited to these specific embodiments.

EXAMPLES l-3 These examples illustrate specific embodiments of a white polyethylene composition according to this invention.

These specific embodiments are formulated as follows:

Concentration in Parts by Wt. Components Ex. 1 Ex. 2 Ex. 3

Normally solid polyethylene 100 100 Finely divided titanium dioxide 5 5 5 4,4.-bis(2,6-di-t-butylpl1enol) O. 5 2,2-methylenebis[G-(I-methyloyclohexyl) -p-cresol] 0. 5 Zinc N,N-dibutyldithiocarbamate 0. 5

EXAMPLE 4 This example illustrates a specific embodiment of a white polypropylene composition according to this invention.

j 3,396,143. I v V V q ,3 This specific embodiment is formulated as follows: Samples .6-8 correspond to the specific embodiments of Examples l-3.

componmtsz gg z g fiz The data show that in the specific compositions of this Normally solidpolypropylene 100 invent on the titan um dioxide pigment and additives Finely difidedmanium dioxide L 5 yn rgl l lly stablllze polyethy ne agaln t the degrad P t Buty1Pheno1 15 two effects of utraviolet light.

In the next series of tests samples were made from This specific embodiment is made by admixing the crystaline polypropylene having an inherent viscosity of components for 5 minutes in a C. W. Brabender Plasto- 1.8. The samples were made by-the procedure described graph. V in connection with Example 4 and included the samples The resulting product is a white plastic composition formulated as indicated by the flowing table. The product suitable for use in shaped articles likely to be exposed obtained in each case was granulated and injection moldto ultraviolet light. ed into -inch tensil bars 2 /2 inches long. Three tensile bars of each samplewere then mounted; under stress in EXAMPLES a %-inch wide channel and the channel placed into the These examples illustrate specific embodiments of a modified Atlas Twin-Arc Weather-Ometer. While exposed composition according to this invention, wherein the to ultraviolet light in this apparatus, the stressed tensile l-olefin resin is a copolymer of propylene and l-butene. bars were periodically inspected for the development of These examples are formulated as follows: stress cracks visible under 3X magnification (Dazor Float- Concentration in Parts by Wt.

Ex. 5 Ex. 6 Ex. 7 Ex. 8' Ex. 9 Ex. 10 Ex. 11 Ex. 12

Components Normally solid copolymer of propylene and l-butene, the weight ratio of propylane to l-butene being 80:20 100 100 100 100 100 100 100 100 Titanium dioxide 5 p-t-Butylphenol 2,2-ruethylenebis[ti-(l-methylcyclohexyl)-p-oresol]- Zinc N-N-dibutyldithiocarbarnate 4,4-bis(2,6-di-t-butylphenol) 4.4-butylidene(6-t-butyl-m-ereso 4,4-thiobis (G-t-butyl-m-cresol) N,N-diphenyl-p-phenylenediamine O. 5

These specific embodiments are made by admixing ing Fixture Model M-209). When such stress cracks for 4 minutes the components on hot compounding rolls, were found to have developed in a specimen, the period the front roll being at 320 F. and the rear roll at of exposure for that specimen was then determined. In 285 F. such fashion the stress crack free life of the sample was The resulting product is a white plastic composition then calculated, it being the averaged exposure times for having utility as a material of construction for shaped all three specimens to develop stress cracks. The test data articles and the like which are likely to be exposed to on the samples here reported are summarized in the folultraviolet light. lowing table.

Actual stability tests have been performed on various 4O specific embodiments of the white plastic composition Sample of this invention. 3 4

In the first series of tests test samples were made from Components: 1 conyentional, low density, normally solid polyethylene 4 orystgmne po1 ypmpy1ene 100 100 100 100 having a melt index of 2. The samples were made by g g d w t l m atas 1.5

pu y p eno the procedure described in connection with Examples 13 stress Crack Free Life (Hm) 140 160 212 633 and included the samples formulated as indicated in the following table. In each case the product obtained was emceutratwnmpms by compression molded into flat plates 125 mils thick. Test Sample 4 corresponds to the specific embodiment of specimens 1.5" x 0.5" were cut from the molded plates, Example bent int U-shape and while so bent were inserted into F m these data it is apparent that titanium dioxide Aa-inch wide channels. While thus under stress, the test and py p cooperate to syflefgistically inhibit specimens were then exposed to ultraviolet light in a traviolet light deterioration of normally solid polypromodified Atlas T-Win-Arc Weather-Ometer [Anal. Chem., py 25 4 0 -1953 r In the next series of tests samples were made according Three test specimens f h sample we employed i to the procedure described in connection with Examples this testing and while exposed to ultraviolet light Were 5-12 from a normally solid copolymer of propylene and periodically examined for the presence of cracks visible l-blltene, Which had a Weight ratio of P py 0 to the unaided eye. When stress cracks had developed in 6 Of 80120, a density of 0- and-34113111561115 Viscosity a specimen, the exposure time of that specimen was deof 2.35. The samples included samplesformulated as inditermined. The stress crack free life of the sample was Gated in the following table. In each case the product obthen calculated, it being the averaged exposure time retained upon preparation of the sample was compression quired for all three specimens of it to develop stress molded into flat plates 125 mils thick. Three test specicraoks. The stress crack free life of the samples reported mens 1.5 inches x 0.5 inch were cut from the molded herein are provided in the following table. plates of the samples, bent into U-shape and while thus Sample No.

Components: 1

Normally solid polyethylene" 100 100 100 100 100 Titanium dioxide (Rutile) 5 5 5 4,4-bis(2,6-di-t-butylphenol) .I 0. 5 0. 5

2,2-methylenebis[fi-(l-methylcyelohexyl)-p cresol] 0 5 0. 5

Zinc N ,N-dibutyldithiocarbamate 0. 5 0. 5 Stress crack free life (Hrs) 329 477 329 342 816 1, 547 997 1 Concentration in parts by weight.

5 6 stressed were mounted in 0.5-inch wide channels. The (A) a normally solid polyethylene, and channels were then placed into the modified Atlas Twina Synergistic stabiiiler Combination r ta ilizing Arc Weather-Ometer. Periodically the specimens were inthe pollethylfine agalnst degradatlve fifiects of ultraviolet light consisting essentially of (1) finely divided titanium dioxide at a concentration of about 0.25-10% by weight of said polyethylene, and

spected for the development of stress cracks visible under r 3X magnification. When stress cracks were detected, the total exposure time for the specimen was then calculated.

The stress crack free life of each sample is the averaged (2 4 4'-bi (2,6-di-t -t butyl phenol) at a concenexposure time required for all three specimens of the tration f about by Weight of Said sample to develop 3X visible stress cracks. The test re- 10 1 h 1 sults on the samples reported herein are summarized in 4. A normally solid white thermoplastic composition the following table. comprising Sample No.

Components: 1

Normally solid copolymer 100 100 100 100 100 100 100 100 100 100 Finely divided titanium dioxide 5 p-t-Bntylphenol 4,4butylidene(G-t-butyl-m-eresol) 4,4-thiobis(fi-t-butyl-m-eresol) 0.5 0.5 N,N-diphenyl-ppenyIenediamine 0. 5 0. 5 Stress crack ireeliteGIrs.) 147 92 140 140 147 238 162 162 185 3,183 162 162 421 280 267 238 289 4,308

1 Concentration in parts by weight.

Samples 11-18 correspond to the specific embodiments (A) a normally solid polyethylene, and of Examples 5-12. (B) a synergistic stabilizer combination for stabilizing From these data it is evident that the compositions of the polyethylene against degradative effects of ultrathis invention are synergistically stabilized against the violet light consisting essentially of degradative efiects of ultraviolet light. (1) finely divided titanium dioxide at a concentra- Thus, there is provided a White plastic composition tion of about 0.25-10% by weight of said polybased on 1titaniuin clliolxidqbwlhich composition has out- (zethzyzlene, arild1 b 6 1 h I h standing n travio et ig tsta ity. met y ene is[ -met ylcyc o exyl)-p- These and other features, advantages and specific emcresol] at a concentration of about 0.1-1.0% bodiments of this invention will be readily apparent to by weight of said polyethylene. those in the exercise of ordinary skill 111 the art upon 5. A normally solid white thermoplastic composition reading the foregoing disclosures. In this connection, comprising while specific embodiments have been described in con- 40 (A) a normally solid olyethylene, a d siderable detail, variations and modifications of these em- (B) a synergistic stabilizer combination for stabilizing bodiments can be effected without departing from the the polyethylene against degradative effects of ultraspirit cand scope of the invention as disclosed and vio(l1e cgnsigticriig essentially 05 c i ne y ivi e titanium dioxi e at a concentra- We claim: tion of about 0.25-l0% by weight of said oly- 1. A normally solid white thermoplastic composition ethylene, and comprising (2) zinc N,N-dibutyl dithiocarbamate at a concen- (A) a normally solid polyethylene, and tration of about 0.11.0% by weight of said (B) a synergistic stabilizer combination for stabilizing polyethylene.

the polyethylene against degradative efiects of ultraviolet light consisting essentially of References Cited (1) finely divided titanium dioxide in an amount UNITED STATES PATENTS if??? to Substantlauy Pgment the Wlyethyl' 2,964,495 12/1960 Newland et al zen-45.75 2 014.0% by Weight of said polyethylene of a 319621606 12/1960 et a1 260-4575 material selected from the group consisting of 596 2/1961 Newland et 2604575 4 i h I Nfils n p enol), 2,2 methyl ene bis[6 (l meth 1 1 h 1 3,325,441 6/1967 McNally et a1 260-41 y cyc o exy p-cresol], and 3,100,197 8/1963 Heuck et al. 260-4595 zinc N,N-d1(C -C alky-l) dithrocarbamate. 3 282 889 11/1966 T 2. A shaped article from the composition of claim 1. om mson 260-4595 3. A normally solid White thermoplastic composition ALLAN LIEBERMAN Prim Examiner comprising ry 

